Combines are old and well known in the art. They are available in various designs and models to perform the basic functions of harvesting, threshing and cleaning of grain or other crop materials.
A typical combine includes a crop harvesting apparatus which reaps planted grain stalks and then feeds the grain stalks to a separating or threshing apparatus. Preferably, the threshing apparatus includes a power-driven rotor mounted inside a stationary cylindrical threshing cage. The rotor threshes and separates the grain from the material other than grain. In such a combine, which has been available for a number of years, the grain is threshed several times repeatedly, but gently, as it spirals around the rotor and passes through openings in the threshing cage. Essentially, most material other than grain stays within the threshing cage and is directed out the rear end of the combine.
While the threshing apparatus acts to separate a substantial portion of the crop or grain from the material other than grain, some chaff or straw is directed out through the openings in the cage along with the grain and a further cleaning or separating action is required. Further separation is normally achieved in a cleaning section.
The cleaning section includes oscillating cleaning sieves. The cleaning sieves are located below the threshing cage to receive the grain and other material expelled from the cage. The oscillation of the sieves arranges the material in a crop mat or veil on top of the sieves. By forcing a stream of air upwardly through the sieves chaff, straw and other lighter material in the crop mat is separated from the heavier grain and is directed out through the end of the combine by the air flow. The heavier seeds or grain fall through the sieves into a collector.
With the increased power and output demands of modern grain combines, cleaning section capacity has become a limiting factor. The most readily achieved method of increasing combine capacity is by increasing the width of the combine and the sieves to spread the crop material across a wider area and in a thinner veil. Increasing the width of the cleaning sieves, so as to increase cleaning section capacity, also involves having to modify the air flow across the increased size of the cleaning sieves. The inherently uneven air distribution of known cleaning fans is accentuated with an increase in the width of the cleaning sieves.
The problem of increased air requirements could, of course, be diminished by increasing the fan diameter in proportion to its increase in its width. This proposed solution, however, is not practical. An increase in fan diameter would necessitate an increase in the height of the combine. The maximum overall height of the machine, however, is dictated by considerations such as clearance under bridges and barn doors. Another reason why the diameter of the fan cannot be increased is that a casing surrounding the fan is the lowest protrusion beneath the combine and, thus, it defines the ground clearance. For proper maneuverability of the combine, it is necessary to maintain adequate ground clearance. The overall height and ground clearance of combines have been reached within their practical limits. Therefore, increasing the diameter of the fan is not a feasible solution to the problem.
One attempt at solving the problem of providing increased air requirements involves a split fan design. With such a design, two fans are mounted on a common shaft. This is an expensive design. Moreover, increases in the width of the cleaning area likewise requires an increase in the fan's length resulting in non-uniform flow output along their length. A non-uniform air flow will be detrimental to proper operation of the cleaning system.
Blower devices commonly known as transverse-flow blowers have a blower wheel which includes a plurality of elongated blades arranged in a cylindrical pattern such that the blower wheel has a hollow interior. The stream of air produced by transverse-flow blowers is relatively thin. Since a combine cleaning system requires a relatively thick stream of air, the use of transverse-flow blowers in combine cleaning system is not a natural adaption.
Transverse-flow blowers are, however, appealing for this purpose because they conserve space and produce a wide uniform stream of air. In such a device, a fan rotor having a series of blades is rotatably arranged within a fan wrapper which encompasses and is closely spaced about the fan rotor. Relatively close tolerances and dimensions are required between the fan wrapper and fan rotor to achieve proper operation of the blower.
Because the blower device on a combine is disposed close to the ground over which the combine moves, the fan rotor, the fan wrapper, or both often engage rocks or other debris causing damage which requires maintenance to the blower. Repeated removal and replacement of such parts often modifies the relationship between the fan wrapper and fan rotor in a manner adversely effecting the performance of the cleaning system. Thus, the overall performance of the combine is often times adversely effected and production falls below an expected level.